NEW: major changes: now possible to output dest2src image and warping field (before only src2dest was done)
NEW: major changes: now possible to output dest2src image and warping field (before only src2dest was done)

Former-commit-id: 7a1ef81d6d35c574b79fbf1d1bf5eb79b6b25cca
Former-commit-id: 7fdc8bcc9cbd08080c0f804f15845aaa5415f6e8
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox